Numerous four-way valve assembles have been developed for controlling both liquids and gases, and such assemblies incorporate a wide range of structural and functional features. Such four-way valve assemblies have, for many years, been of substantial size and have often incorporated multiple shiftable valves in order to provide for proper control over fluid flow. Modern technology, however, has increasingly demanded that such valve assemblies be made of extremely small and compact size, particularly when such assemblies are utilized in pneumatic control circuits and the like, and in addition such assemblies must be capable of permitting shifting of the valve with extremely small forces without detracting from the desired response time.
One of the common problems associated with many known four-way valves, particularly when they utilize shiftable valves of the poppet type, has been the fact that such assemblies often require at least two poppet-type shiftable valve stems in order to provide the desired structural and functional relationships. The use of multiple shiftable valve stems increases the structural complexity of the valve assembly, including both the size and functional characteristics, and also significantly increases the manufacturing cost. The use of multiple valve stems also increases the number of wear points subject to failure and/or maintenance.
Another problem encountered with conventional four-way valve assemblies, including those which use either single or multiple shiftable valve stems, has been the difficulty in achieving a minimum shifting force. The valve industry has, for many years, attempted to improve valve operation by providing at least a partial pressure balance upon the shiftable valve stem so as to minimize shifting forces. This balance is achieved by locating the seals and pressure areas in such manner as to avoid the application of large unbalanced pressure forces on the shiftable valve stem. While great strides have been made in achieving at least a partial balance on the shiftable valve stem, nevertheless this goal is not always optimized in view of the overall structural and functional relationships which exist between the shiftable valve stem and the other operational characteristics of the assembly.
Still another problem associated with known valve assemblies, particularly in those assemblies which are of extremely small size so as to be suitable for use in control systems, such as pneumatic control circuits, is the difficulty in maintaining proper tolerances including concentric relationships between the shiftable valve stem and its housing so as to permit optimum performance including minimization of shifting force. This precision of manufacture has often been compromised in view of difficulties in achieving such manufacture, or at least the impracticality of doing so at reasonable cost.
Accordingly, it is an object of the present invention to provide an improved four-way valve assembly which greatly improves upon, and in fact overcomes, many of the disadvantages associated with prior structures as briefly described above.
More specifically, it is an object of the present invention to provide an improved four-way valve assembly which is highly desirable for use in controlling flow of a gas, such as for use in a pneumatic control system, by employing a single shiftable valve for controlling the four flow functions, which is of an extremely small and compact spacial arrangement, and which can be economically manufactured and assembled while maintaining and utilizing a shiftable valve of extremely small cross-sectional size while maintaining desirable tolerances and sliding fits.
It is also an object of the invention to provide an improved four-way valve assembly, as aforesaid, which is capable of providing an extremely small shifting force, both due to the manner in which the shiftable valve is slidably supported, and due also to the achievement of a pressure balance which is at least of a high degree so as to permit prompt and rapid shifting while employing a minimal shifting force.
In the improved four-way valve assembly of the present invention, and specifically in the preferred embodiment thereof, there is provided a housing having an elongate bore in which is slidably disposed a single shiftable valve of the poppet type. The housing includes a main center housing part and a pair of end housing parts which removably attach to opposite ends of the center part and cooperate therewith for defining the elongate bore. A pair of sleevelike liners are stationarily disposed in the bore and cooperate with the housing for defining an inlet port which communicates with the bore in the region between the adjacent ends of the liners, and a pair of load ports which communicate with the bore through the individual liners and are spaced axially on opposite sides of the inlet port. A pair of exhaust ports are provided in the housing, one in each end housing part, for communication with the bore. The single valve has a poppet mounted centrally thereof and disposed so as to axially shift between and sealingly coact with valve seats formed on the opposed inner ends of the liners. The opposite free ends of the valve are slidably supported within seal rings, such as cup seals, which are mounted on the end housing parts outwardly from the respectively adjacent exhaust ports to maintain a pressure balance on the valve stem. Each of the liners has a sleevelike hub part at its outer end which projects outwardly beyond the center body part and is received within the bore of the respectively adjacent end housing part so that the latter is concentrically seated on this hub part.
Other objects and purposes of the invention will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.